Our Board Scientists Answer Questions about Corn, Milk, and Sour Cream

Wonder no more.  The answers to  some common  kitchen questions (mine and yours) are paraphrased directly below the questions, thanks to the five scientists who serve on the Shelf Life Advice Advisory Board. I think you'll find their responses useful and enlightening.   It's also reassuring to see that our scientists (who come from 5 different states and rarely or never meet) generally agree on the best advice for serving safe, nutritious, delicious food.




(1) Can I refrigerate leftover cooked corn on the cob and then reheat and serve it a day or two later?  If so, should I wrap each piece individually in plastic or aluminum foil or just put all the leftover pieces in one bag and seal tightly?  Would reheated corn be safe to eat but of inferior quality? 


Food scientist Dr. Karin Allen: Store leftover corn on the cob in a Ziplock bag.  There's no need to wrap each cob separately.  Microwaves heat inconsistently (unevenly), so never reheat corn in a microwave oven.  Reheat on the stovetop in boiling water.  Reheated corn may not be quite as delicious as the first time  around, but, if you put enough butter on it, it will still taste good.


Food process engineer Dr. Timothy Bowser: For leftover corn on the cob, it’s best to cut off the corn kernels and use them in recipes such as creamed corn, salad, corn fritters, salsa, etc. You can refrigerate leftover corn on the cob and reheat it for the next meal if you want, but unless the corn was cooked very lightly, it will be soft and perhaps even mushy. If the corn was just blanched, or barely cooked, I would vacuum-pack the cobbs or wrap them in something like cling-wrap (to keep out the air) and then slip them into a bag with a zipper closure for additional protection before freezing or refrigerating.


Food scientist Dr. Catherine Cutter:  Reheated corn will be safe to eat but the quality may degrade a little. The kernels may become mushy.  I recommend cutting off the kernels and using them in something like salsa, chili, or soups such as corn or clam chowder.  If you want to freeze the leftover corn, remove the corn from the cob and place the kernels in a zip-lock freezer bag.


Food scientist Dr. Clair Hicks: Cooked corn on the cob can be refrigerated and used within the next couple of days.  Only reheat what is going to be eaten.  Don't reheat twice.


Food Scientist Dr. Joe Regenstein: You certainly can save leftover corn. I don’t like storing things directly in aluminum. Plastic wrap, I believe, can be used directly.  Reheating  probably lowers the quality of the corn a little, but using the kernels in salads is fine.


EDITOR'S NOTE: "The use of aluminum foil for cooking contributes significantly to the daily intake of aluminum through cooked foods. The amount of leaching is high in acidic solutions and even higher with the addition of spices. Excessive consumption of aluminum from leaching aluminum foil has extreme health risks. Aluminum foil may be used for packing but not for cooking." according to the  International Journal of ELECTROCHEMICAL SCIENCE.   In short, don't wrap foods in aluminum foil for cooking.  Resist the urge to do this with chicken parts, corn on the cob, whole potatoes, and so on even if you've been doing it for  years.  Read more about this topic at electrochemsci.org   Other online sources also cover the risks of cooking with aluminum foil.  For example, check out this Huffington Post  article: "Why You Shouldn't Wrap Your Food in Aluminum Foil Before Cooking It." It says that foods most likely to absorb more aluminum are spicy or acidic foods cooked at high temperatures. Wrapping cold food in aluminum foil is okay for a short time.




(2) Is it safe to refrigerate leftover milk in a glass or small pitcher?  Should I put it in an ice bath to cool it down before refrigerating, or should I just discard the unused warm milk? Will reheated milk have an off-taste?  Will the vitamin content be decreased?


Dr. Karin Allen: Don't heat and cool milk more than once. Put warm milk in a container that exposes a lot of surface to cooling, for example a short, wide container. If milk is heated on the stove and gets scorched, it won't taste good.  Heat it in the microwave. 


Dr. Timothy Bowser:  Milk that has been reheated should be discarded if it has remained at warm temperatures (above 140°F) for a significant time period because bacteria will grow rapidly. If leftover, heated milk has not been sitting around and is quickly chilled (in an ice bath), then it should be okay to refrigerate and reuse. Some people prefer the cooked taste of milk, while others do not. In either case, the quality of the milk will be reduced by additional heating. That is, vitamins and enzymes that are susceptible to destruction from heat  may be destroyed.  


High heat (like the temperatures of pasteurization) will kill microorganisms, but it can also denature enzymes. Lipase is an example of an enzyme in milk that can aid in the digestion of fats. However, lipase breaks down quickly under pasteurization. To learn more about enzymes in milk, click here:

 http://www.raw-milk facts.com/enzymes_T3.html


Dr. Catherine Cutter: The quality of milk deteriorates somewhat as a result of reheating.  If you reheat milk over and over, some of  its desirable qualities will disappear.  To cool it down quickly before refrigerating, place the container in some icy water until the milk in it reaches 40°F.  Cooked milk may have a slight caramel or burnt flavor, depending upon the length of cooking time and/or the temperature it's heated to. 

Dr. Clair Hicks: Try to heat only as much milk as you are going to use.  Every time milk is heated to lower than pasteurization temperatures, bacteria begin to grow at an accelerated pace. Flavor is also affected.  I certainly would not recommend that milk be heated and cooled several times.  

Dr. Joe Regenstein: It would depend on the temperature.  If it was heated above 140°F and not left in the danger zone for very long, it would be fine for about 2 hours. If you heat it high enough you will get cooked milk flavor. Most people don’t like it, but evaporated milk has this flavor, and many farmers who pasteurize at home may let milk overheat to achieve the cooked milk flavor. One of my college roommates did that. He’d bring “fresh milk from home.” He thought the cooked milk flavor was better than other milk!


EDITOR'S NOTE: Change can occur in the taste and odor of milk as a result of one or more of  these processes: absorption, microbial contamination, or chemical contamination. For example, milk can absorb off-flavors from a poorly ventilated barn or a smelly refrigerator (especially if the milk container is made of paperboard).  Bacterial causes may result from improper cooling.  Chemical defects in the quality of milk can occur from exposure to sunlight or fluorescent lights or even cleaning chemicals or medicines, among other causes.  Milk can take on many different off-flavors including acidic, barny, bitter, garlicy, and metallic. 




(3) My carton of Daisy sour cream has this message on the cover of the inner foil  wrap: "To  prolong freshness, completely remove and discard this foil seal." I've never seen this sort of message on sour cream before. How can the foil hurt the product?


Dr. Allen:  When you remove the outer lid, you're not contaminating the food.  But when your fingers work with the inner liner, you could be depositing bacteria on the lid from your hand or the air. This may not be the reason for Daisy's warning, but it's a logical possibility.  Here's another possible reason for the warning about removing the foil: Aluminum foil is especially likely to leach into foods with lower pHHHh    H, that is, with greater acidity). Therefore, it's more important to keep foil away from sour cream than it would be to keep it from touching cottage cheese because cottage cheese is less acidic.


Why is there an inner foil or plastic on the product in the first place?  It keeps oxygen out and moisture in.  Also, if the lid comes loose, the inner liner prevents accidental contamination. 


Dr. Bowser: Once the foil seal is broken or peeled back, it is no longer needed. The purpose of the seal is to keep air out. It will not reseal after it has been peeled back. The seal could get in the way of the lid as the plastic lid is now the primary seal for the container. Also, dried sour cream and bacteria on the foil seal could find its way into the sour cream, so it is best to remove the foil seal.


Dr. Cutter: Aluminum foil may leach into foods, especially dishes made with lemon juice or

spicy food.  Many companies use a plastic inner seal rather than foil.


Dr. Hicks: You can get an acid reaction with the foil causing discoloration and some off- flavor development, so it's best to get it out of the way.  The top surface of the foil may not be coated, so it could react much faster than the bottom side of the foil.


Dr. Regenstein: Direct contact with aluminum in the presence of air/oxygen may lead to reactions that will give a negative flavor.




electrochemsic.org  International Journal of ELECTROCHEMICAL SCIENCE  "Risk Assessment of Using Aluminum Foil in Food Preparation"  http://www.electrochemsci.org/papers/vol7/7054498.pdf



Contributing Shelf Life Advice Advisory Board Members:


Karin E. Allen, Ph.D., Utah State University, Dept. of Nutrition, Dietetics, and Food Sciences


Timothy J. Bowser, Ph.D. , Oklahoma State University, Dept. of Biosystems and Agricultural Engineering


Catherine Nettles Cutter, Ph.D. , Pennsylvania State University, Department of Food Science


Clair L. Hicks, Ph.D., University of Kentucky, Dept. of Animal and Food Sciences


Joe Regenstein, Ph.D., Cornell University, Dept. of Food Science



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